The present inventions relate generally to mechanisms for controlling the standoff distance between an optical fiber and a photonic device in an optoelectronic package. More particularly, a dam structure that defines the standoff distance between the photonic device and the optical fiber(s) is described.
Optical networks have a wide variety of applications and are, for example, widely used within the telecommunications, data transmission and high speed networking industries. The optical devices used to convert electrical signals into light signals and light signals into electrical signals are key components in any such optical network. Generally, such devices include one or more photonic elements (e.g. detectors and/or laser emitters) together with the electronic circuitry necessary to drive the photonic elements (e.g., receiver, transmitter or transceiver circuitry). Although a wide variety of optical transceiver devices are currently commercially available, there are always continuing efforts to improve their design and functionality as well as to lower their production costs.
One issue that is fundamental to the design of any photonic device is the desire to (relatively) efficiently optically couple each active facet (i.e., emitter or detector) to its associated optical fiber. The coupled power on launch (lasing) must be enough to supply the complete linkxe2x80x94with the detector receiving enough power to resolve a signal, but not so high that laser safety is compromised. It is often considered desirable to place the optical fiber as close as possible to the active region (facet) of the photonic device. However, there are often practical limits to this. By way of example, in some devices, there is a concern that if the optical fiber physically contacts the photonic element, it may cause physical damage to the photonic device. Further, in some devices, the photonic device is electrically connected to a substrate by wire bonding and placing the optical fiber too close to the photonic device may risk damaging the bonding wires. Therefore, it is common in today""s implementation schemes to maintain a relatively large standoff distance between a photonic device and its associated optical fiber(s). By way of example, standoff distances on the order of 1 to 5 millimeters are typical in commercial systems that are presently available. At these distances, it becomes important to collimate the optical fibers to insure good optical coupling between the fibers and the photonic elements. Typically collimation is accomplished by providing a simple lens at the termination of the optical fiber at emitter or detector active regions, or both
One approach to maintaining a close coupling between the photonic device and the optical fiber is to control the standoff distance between the two components. This can be done, by placing a spacer on the base that supports the photonic device. Although the use of a spacer has significant appeal (and indeed the approach can be used with success), there are some practical drawbacks to this approach. Most notably, it can be difficult to provide precise quality control of the standoff distance.
When an integrated circuit wafer is fabricated, it will have a designated nominal thickness. However, as a practical matter there tend to be thickness variations between different photonic wafers, which results in thickness variations in their respective dice. More particularly, photonic wafers are typically background to a desired thickness. However, the typical grinding process is accurate only to within about 0.5 mil (13 microns) of the targeted thickness. Thus, different wafers may have different thickness, and mixing dice from these wafers will potentially impact the ability to accurately obtain the desired fiber standoff. Therefore, in a transceiver configuration, detector and laser die must be pre-measured for thickness xe2x80x98pairingxe2x80x99. Similarly, when a spacer is fabricated, there are spacer production tolerances as well (although the spacer production tolerances tend to vary less than the wafer thickness). If the die thickness varies too much, there may be production problems using a spacer to provide the desired standoff between the die and optical fiber. For example, if the die is too thin relative to the spacer, then the gap between the fiber and the active facet may be farther than desired which reduces optical coupling. Alternatively, if the die is too thick relative to the spacer, then the gap is too small which may result in mechanical damage during the assembly process. One approach to addressing these tolerance problems is to sort and match the dice and spacers to provide the desired standoff.
Although the described systems for controlling standoff work well, they are relatively expensive to produce. Sorting and matching die thickness can be quite time consuming, costly, and can present real logistical issues in terms of binning the die inventory. Accordingly, there are continuing efforts to provide improved optical component packaging techniques that help reduce the size and costs of the optical components.
To achieve the foregoing and other objects and in accordance with the purpose of the present invention, an optoelectronic component is described that includes a photonic device carried by a base substrate. A dam structure is formed on the base substrate by dispensing and hardening a precise amount of a flowable material. The dam structure is sized to define a desired standoff between an optical fiber and an active facet on the photonic device.
In various embodiments, it may be desirable to provide a plurality of dam structures. In some preferred embodiments, the dam structure(s) is formed from an epoxy based material.
In some embodiments, the base substrate takes the form of a flexible material having electrically conductive traces thereon that are electrically connected to the photonic device. An optical component support block may be provided to support the flex material. In some implementations, a semiconductor die may be directly soldered to the traces on the flexible material. In other implementations, the base substrate is a ceramic form printed with electrically conductive traces.
In embodiments where the photonic device is wire bonded to the base substrate, it may be desirable to provide a reverse wire bond in order to permit the optical fiber to be placed closer to the photonic device.